Wafer polishing head

ABSTRACT

A wafer polishing head according to the invention is disclosed. In the wafer polishing head, an automatic control device is additionally installed outside the wafer polishing head for automatically adjusting a pressure applied on a retaining ring. This ensures the bottom of the retaining ring always lower than that of a carrier, thereby preventing a semiconductor wafer from slip during polishing. Furthermore, a liquid pressure generated to press the carrier can efficiently alleviate wabble during polishing. Therefore, the wafer polishing head of the invention can greatly improve a polishing uniformity.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of a prior application Ser. No.09/741,072, filed Dec. 21, 2000. The prior application Ser. No.09/741,072 claims the priority benefit of U.S. Pat. No. 6,220,930 B1,issued on Apr. 24, 2001. The U.S. Pat. No. 6,220,930 B1 is acontinuation-in-part of a prior application Ser. No. 09/185,098, filedNov. 3, 1998. All disclosure of the prior patent and applications areincorporated herein by references.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a chemical mechanical polishing (CMP) device,and in particular to a wafer polishing head controlled by gas and liquidpressures.

2. Description of the Related Art

Chemical mechanical polishing (CMP) is a global planarization technique.In chemical mechanical polishing, the rear surface of a semiconductorwafer is fixed by a wafer polishing head. Then, the front surface of thesemiconductor wafer is pressed against a polishing pad which isinstalled on a removable platen. When polishing, a chemical agentconducive to CMP is continuously supplied to the platen. By the chemicalreaction between the chemical agent and the front surface of thesemiconductor wafer and mechanical polishing, the front surface of thesemiconductor wafer can be completely planarized.

The wafer polishing head is used to safely and firmly hold thesemiconductor wafer without any damage or contamination on thesemiconductor wafer. In an early phase, a semiconductor wafer wasadhered on a carrier with a material like wax. After polishing, the waxmust be completely removed or the semiconductor wafer is contaminated.Currently, a wafer adhering layer is additionally disposed on the bottomof the carrier. Since the wafer adhering layer is made of a porousmaterial, a semiconductor wafer can be firmly held on the carrier bycreating a vacuum environment. However, a high-speed rotation couldcause the semiconductor wafer slipping during polishing. Therefore, aretaining ring is additionally installed to surround the semiconductorwafer, thereby preventing the semiconductor wafer from slip. Theretaining ring must be rigid and uneasily react with any chemical agent.Typically, Delrin and Tecktron are used to make the retaining ring.

FIG. 1A is a cross-sectional view illustrating a wafer polishing head 10according to the invention. Referring to FIG. 1A, a carrier 12 is a mainbody of the wafer polishing head 10. A wafer adhering layer 14, made ofan adhesive and porous material like felt, is disposed on the bottom ofthe carrier 12. Since the wafer adhering layer 14 is porous, the rearsurface of a semiconductor wafer 16 can be firmly held on the waferadhering layer 14 by creating a vacuum environment during wafer loading.A retaining ring 18 surrounds the carrier 12 and the semiconductor wafer16, wherein the bottom of the retaining ring 18 must have a lowerposition than that of the carrier 10, such that the semiconductor wafer16 can be prevented from damage during polishing. Furthermore, a firstpressure chamber 20 is disposed directly above the retaining ring 18. Adiaphragm 22 is disposed on the bottom the first pressure chamber 20 andcontact the retaining ring 16. When a gas flows into the first pressurechamber 20, the diaphragm 22 is deformed to press again the retainingring 18, thereby fixing the retaining ring 18. A second pressure chamber24 is disposed directly on the carrier 12. When a gas flows into thesecond pressure chamber 24, a force is created to push the semiconductorwafer 16 via the carrier 12.

FIG. 1B is a flow chart illustrating a pressure control of the waferpolishing head 10 of FIG. 1A. In FIG. 1B, a gas source 26 supplies arequired gas to the first pressure chamber 20, the second pressurechamber 22 and the carrier 12.

During polishing, the retaining ring 26 always contacts the diaphragm22, resulting in an abrasion therebetween. Under this condition, it iseasy to cause the semiconductor wafer 16 slipping if the bottom of thecarrier 12 is lower than that of the retaining ring 18. To resolve thisproblem, it is necessary to regularly adjust the retaining ring 18thereby to maintain the bottom of the retaining ring 16 at a lowerposition than that of the carrier 10.

As can be obviously seen from the above, the prior wafer polishing headuses a gas pressure to provide a vertical force to the semiconductorwafer and the polishing pad, thereby alleviating wabble duringpolishing. However, the gas pressure depends on the stability of the gassource. As a result, it is easy to cause wabble on the semiconductorwafer and the polishing pad, resulting in a poor polishing uniformity.Moreover, the retaining ring always contacts the polishing pad, causingan abrasion therebetween. In this case, it is easily to make thesemiconductor wafer slip if the bottom of the carrier is lower than thatof the retaining ring. To overcome this problem, the retaining ring mustbe regularly and manually adjusted to an appropriate position, andpressures generated by a gas to press the carrier and the retaining ringare also manually adjusted to different proper pressure values eventhough the gas comes from the same gas source.

SUMMARY OF THE INVENTION

In view of the above, an object of the invention is to provide a waferpolishing head which uses a liquid pressure to press a carrier therebyto obtain a better polishing uniformity. Furthermore, a pressure appliedon a retaining ring is automatically adjusted by an automatic controldevice, thereby allowing the retaining ring to efficiently prevent asemiconductor wafer from slip during polishing.

As to the wafer polishing head according to the invention, an automaticcontrol pressure device, which is additionally installed outside thewafer polishing head, can automatically adjust a pressure applied on aretaining ring, thereby ensuring a polished semiconductor wafer does notslip away. In addition, the wafer polishing head can greatly alleviatewabble on the carrier by using a liquid pressure to press the carrier.Accordingly, the wafer polishing head of the invention can greatlyimprove a polishing uniformity.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only, and thus do not limit the presentinvention, and wherein:

FIG. 1A is a cross-sectional view illustrating a wafer polishing headaccording the prior art;

FIG. 1B is a flow chart illustrating a pressure control of the waferpolishing head of FIG. 1A;

FIG. 2A is a cross-sectional view illustrating a wafer polishing headaccording to a preferred embodiment of the invention; and

FIG. 2B is a flow chart illustrating a pressure control of the waferpolishing head of FIG. 2A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2A is a cross-sectional view showing a wafer polishing head 60according to a preferred embodiment of the invention. In FIG. 2A, acarrier 62 is disposed at the center region of the wafer polishing head60. A wafer adhering layer 64, such as a porous plank like felt, isdisposed beneath the carrier 62. Like the prior art, the rear surface ofa semiconductor wafer 66 can be firmly held on the wafer adhering layer64 in a vacuum environment. A retaining ring 72 surrounds the carrier62, wherein the bottom of the retaining ring 72 must be maintained lowerthan that of the carrier 62. Moreover, a first pressure chamber 68 isdisposed directly above the retaining ring 72 with a diaphragm 70therebetween against the retaining ring 72. A second pressure chamber 74is disposed directly on the carrier 62 and partly filled by a liquid 76,such as silicon oil, which has low volatility and chemical reactivity.

Referring to FIG. 2B, a gas source 80 supplies a required gas to thefirst pressure chamber 68 and the second pressure chamber 74. To controlthe pressure of the first pressure chamber 68, a gas coming from the gassource 80 must be first adjusted by an automatic control pressure device90, and then transmitted to the first pressure chamber 68. As an examplein the embodiment, the automatic control pressure device 90 consists ofa converter 92, a controller 94 and a pressure regulator 96. Withrespect to the control flow of the wafer polishing head 60, a pressuresignal generated by the first pressure chamber 68 is first transmittedto the converter 92, such as an analog/digital (A/D) converter. Thepressure signal is converted to a digital signal by the converter 92,and then transmitted to the controller 94. After the digital signal iscalculated and compared to a set value by the controller 94, thecontroller 94 transmits an electronic signal to the pressure regulator96, such as a control valve, thereby controlling a gas flow to the firstpressure chamber 68 from the gas source 80. Thus, the diaphragm 70 canbe deformed to apply a proper pressure on the retaining ring 72. As aresult, the bottom of the retaining ring 72 is frequently maintainedlower than that of the carrier 62, thereby preventing the semiconductorwafer 66 from slip. Moreover, a gas flowing to the second pressurechamber 74 from the gas source 80 plus the liquid 76 therein creates aliquid pressure on the semiconductor wafer 66.

In summary, the advantages of the wafer polishing head according to theinvention are as follows:

(1) A polishing uniformity is greatly improved since the liquid pressuregenerated to press the carrier can efficiently alleviate wabble, andmake the carrier and the semiconductor wafer parallel to each other.

(2) The retaining ring is adjusted by the automatic control pressuredevice without manual adjustments. This ensures that the bottom of theretaining ring is always lower than that of the carrier. Therefore, thesemiconductor wafer can be well protected during polishing and thelifetime of the retaining ring is extended.

While the invention has been described by way of example and in terms ofthe preferred embodiment, it is to be understood that the invention isnot limited to the disclosed embodiment. To the contrary, it is intendedto cover various modifications and similar arrangements as would beapparent to those skilled in the art. Therefore, the scope of theappended claims should be accorded the broadest interpretation so as toencompass all such modifications and similar arrangements.

1. A wafer polishing head for planarizing a wafer comprising a carrierfor loading the wafer, a wafer adhering layer disposed beneath thecarrier, a retaining ring surrounding the carrier and the wafer adheringlayer, the wafer polishing comprising: a first pressure chamber having afirst inner pressure disposed above the retaining ring; a secondpressure chamber having a second inner pressure disposed on the carrier;and an automatic control system respectively coupled to the firstpressure chamber and the second pressure chamber for adjusting arelative height between the carrier and the retaining ring.
 2. A waferpolishing head for planarizing a wafer comprising a carrier for loadingthe wafer, a wafer adhering layer disposed beneath the carrier, aretaining ring surrounding the carrier and the wafer adhering layer, thewafer polishing comprising: a first pressure chamber having a firstinner pressure disposed above the retaining ring; and a second pressurechamber having a second inner pressure disposed on the carrier, whereina relative height between the retaining ring and the carrier can beadjusted by changing the first and second inner pressure.
 3. A waferpolishing head for planarizing a wafer comprising a carrier for loadingthe wafer, a wafer adhering layer disposed beneath the carrier, aretaining ring surrounding the carrier, the wafer adhering layer, afirst pressure chamber having a first inner pressure disposed above theretaining ring, and a second pressure chamber having a second innerpressure disposed on the carrier, the wafer polishing comprising: anautomatic control system respectively coupled to the first pressurechamber and the second pressure chamber for adjusting a relative heightbetween the carrier and the retaining ring.